Introduction to Pathology: Hemodynamic Disorders

Introduction to Pathology

• Pathology is the study of disease.
• Dr. Raya D. Marji, M.D. is the instructor.
• Office: 0-505
• Email: [email protected]

Hemodynamic Disorders

• Hemodynamic disorders include hyperemia and congestion, edema, hemorrhage, and hemostasis and thrombosis.

Hyperemia and Congestion

• Hyperemia is an increase in blood volume within a tissue, caused by arteriolar dilation and increased blood flow. It appears red.
• Congestion is a passive process resulting from impaired outflow of venous blood from a tissue. It appears blue-red (cyanosis).
• Chronic congestion can lead to hypoxia, parenchymal cell death, secondary tissue fibrosis, and edema. It can even rupture capillaries, causing focal hemorrhages.

Edema

• Edema is the accumulation of fluid within tissues.
• 60% of lean body weight is water, two thirds of which is intracellular.
• Only 5% of the body's water is in blood plasma.
• Edema can be generalized or localized.
• Causes of edema include increased hydrostatic pressure, reduced plasma osmotic pressure, and lymphatic obstruction.
• Causes of increased hydrostatic pressure include impaired venous return (like congestive heart failure, constrictive pericarditis, ascites) and arteriolar dilation (like heat).
• Reduced plasma osmotic pressure is often related to low protein and albumin (as in nephrotic syndrome, cirrhosis or malnutrition).
• Obstructions in lymphatic drainage due to inflammatory conditions, neoplastic conditions or surgery can also cause edema.

Hemorrhage

• Hemorrhage is the extravasation (escape out) of blood from blood vessels, often caused by damage to blood vessels or impaired clot formation.
• Causes can include trauma, atherosclerosis, or inflammatory or neoplastic vessel wall erosion.
• Hemorrhage can impact the body in profound ways, including shock from blood loss or potential death due to damage in vital organs (especially the brain).
• Hemorrhagic diatheses are diverse diseases of vessel walls, platelets, or coagulation factors leading to unusual bleeding.

Hemostasis and Thrombosis

• Normal hemostasis is the body's controlled process of blood clotting to stop bleeding from an injured vessel.
• Thrombosis is the pathological formation of a blood clot (thrombus) in a non-injured vessel.
• Normal hemostasis involves platelets, coagulation factors, and endothelium to constrict arterioles, forming a platelet plug and ultimately a fibrin clot that will block further bleeding.
• Blood clot breakdown is called fibrinolysis.

Morphology of Edema, Hemorrhage and Congestion

• Edema is easily recognized on gross inspection, with swelling. Microscopic examination reveals clear tissue and separated ECM components (often the surrounding tissue will retain some water).
• Dependent edema is most noticeable in the legs and sacrum due to high hydrostatic pressure.
• Tissues affected by congestion have altered appearances (colour, texture). Congested lungs have blood in the alveoli.
• Chronic passive liver congestion: the central regions are red-brown and depressed. Microscopically, there is centrilobular hepatocyte necrosis, hemorrhage and macrophages.

Clinical Features of Edema, Hemorrhage and Congestion

• Subcutaneous edema is an indicator of fluid retention problems, often systemic.
• Pulmonary edema is associated with various conditions, and can be life-threatening due to respiratory impairment.
• Brain edema presents as hazardous swelling in the head and can cause herniation.